Think about it:
•*More Mac-like than the iPhone, with large storage, strong processor, and large screen
•*the iPhone SDK is coming out end of February, essentially creating a new development platform, based on OSX (making it easy for developers to port existing apps)
• iPhone gestures as an interface - image turning a page by swiping your finger across it!
• Spotlight search
•*OS X already does handwriting recognition with the INK application
• Leopard sharing features
•*Easy sync through iTunes
• Apple's ability to leverage publisher's for content deals

Granted, it would not be eInk based, but it is amazing how readable PDFs are on the tiny iPhone screen, I can only imagine them on a tablet sized device! And a built in backlight makes night reading more convenient as well. I would trade eInk for the advantages of a Mac Tablet.